1. Field
The presently disclosed subject matter relates to a semiconductor light emitting apparatus which emits light from semiconductor light emitting devices through a wavelength converting material and a light diffusing material.
2. Description of the Related Art
Conventionally, semiconductor light emitting apparatuses have been disclosed, for example, in Japanese Patent No. 3,690,968 (corresponding to Japanese Patent Application Laid-Open No. 2001-077433) and Japanese Patent Application Laid-Open No. 2006-165416.
More specifically, in Japanese Patent No. 3,690,968, a semiconductor light emitting apparatus is configured to include the following: a substrate having a cavity in its surface; a semiconductor light emitting device mounted on the cavitied-surface of the substrate, or into the cavity recess; and a translucent mold member filled in the cavity recess, the material containing a fluorescent material and a light diffusing material.
In this instance, the above mentioned fluorescent material has a specific gravity higher than those of the translucent mold member and the diffusing material. In the translucent mold member which is cured inside the cavity recess, it is possible to provide a concentration gradient of the fluorescent material. Accordingly, the fluorescent material increases in concentration as it approaches the semiconductor light emitting device below. The light diffusing material increases in concentration as it approaches the top of the translucent mold member above.
According to the semiconductor light emitting apparatus having such a configuration, when the semiconductor light emitting device emits light, the light from the semiconductor light emitting device is incident on the fluorescent material to excite the fluorescent material. As a result, the fluorescent material emits fluorescence with a predetermined color, which is scattered by the light diffusing material and emitted outside from the surface of the translucent mold member.
In this instance, the light diffusing material is configured to have a function of reflecting light from outside and a function of scattering fluorescence that is emitted from the fluorescent material when excited by the light emitted from the semiconductor light emitting device.
On the other hand, the semiconductor light emitting apparatus disclosed in Japanese Patent Application Laid-Open No. 2006-165416 is manufactured by the following process steps. An open-ended hollow lamp house having openings shaped like numerals, letters, or the like in its surface is placed with the surface side down. Then, a transparent resin material containing a diffusing material and a fluorescent material is injected into the hollow area of this lamp house. Next, electrode members having an LED chip mounted thereon are set into the hollow area of the lamp house. In this state, the lamp house is put into a constant-temperature bath to precipitate the fluorescent material on the surface side, and the transparent resin material is cured to complete the semiconductor light emitting apparatus.
In either of the semiconductor light emitting apparatuses disclosed in Japanese Patent No. 3,690,968 and Japanese Patent Application Laid-Open No. 2006-165416, the translucent mold member or the transparent resin material (light transmitting resin) is mixed with a fluorescent material and cured. In this case, the fluorescent material precipitates by gravity based on a difference between the specific gravities of the light transmitting resin and the fluorescent material, thereby forming a fluorescent material layer having a high concentration of fluorescent material.
Nevertheless, in the semiconductor light emitting apparatus disclosed in Japanese Patent No. 3,690,968, the fluorescent material is also deposited on areas of the substrate surface other than the semiconductor light emitting device. Accordingly, these areas are higher in the concentration of the fluorescent material as compared to the top of the semiconductor light emitting device. Namely, this area of fluorescent material causes higher fluorescence when the semiconductor light emitting device is lighted, as compared to the fluorescence from the top of the semiconductor light emitting device.
For example, when a combination of a blue light emitting device and a yellow fluorescent material is used in this type of semiconductor light emitting apparatus for achieving white light, this configuration can result in more yellowish color, causing color variations in terms of the entire light emitting surface of the semiconductor light emitting apparatus.
Because these areas are located around the light emitting device, the light emitted from the device cannot enter these areas easily. Accordingly, these areas are low in the intensity of excitation by the semiconductor light emitting device in spite of the high concentration of the fluorescent material. This lowers the intensity of the fluorescence, causing significant intensity variations in terms of the entire light emitting surface of the semiconductor light emitting apparatus.
Moreover, if a diffusion sheet is overlaid on the light emitting surface of the foregoing semiconductor light emitting apparatus for the purpose of a backlight intended for a liquid crystal display, the color variations and the intensity variations mentioned above can be reduced comparatively. Nevertheless, when high-current power LEDs are used as the semiconductor light emitting device and built into the optical system of a reflector, projector, and the like, the foregoing color variations and intensity variations may appear in greater significance and may deteriorate the quality of the semiconductor light emitting apparatus used as a light source.
In the semiconductor light emitting apparatus disclosed in Japanese Patent Application Laid-Open No. 2006-165416, the fluorescent material is deposited only in the display areas of the numerals, letters, etc. The fluorescent material varies in concentration, however, depending on the shapes and dimensions of the display areas. The apparatus causes color variations and intensity variations similarly, and thus cannot be used as a surface light source.